In a rotating electrical machine conventionally made of a rotor and a stator, the stator is formed of a stator core having a plurality of slots formed therein, and a coil wound around teeth provided between the slots, while the rotor is formed of a rotor core made of a plurality of stacked magnetic steel sheets, a magnetized permanent magnet, and a shaft serving as a rotating shaft. When power is supplied to the coil, a magnetic field is generated. Based on the generated magnetic field, a magnetic flux flows between the rotor and the stator, and thereby the rotor obtains turning force. The permanent magnet is inserted into an opening provided in the rotor core to be fixed to the rotor core with an adhesive. End plates are provided to sandwich the rotor core in a direction of a rotation axis of the rotor.
As to the rotating electrical machine with such a structure, Japanese Patent Laying-Open No. 2003-199303, for example, discloses a method of manufacturing a motor, the method ensuring the strength of an embedded magnet rotor, maintaining the property of the motor, and allowing a permanent magnet to be coated. The method of manufacturing a motor shows a method of manufacturing a motor formed of a stator and a permanent magnet rotor. The permanent magnet rotor is made such that an approximately cylindrical rotor core made of a material having a high magnetic permeability, such as iron, is provided with a plurality of holes each penetrating the rotor core in its axial direction for embedding a permanent magnet, and that a permanent magnet is then embedded in each of the plurality of holes. This motor rotates owing to a rotating magnetic field generated by a current flowing through a wire provided at the stator. In the method of manufacturing the motor, a permanent magnet is directly coated with an adhesive, and thereafter bonded to the rotor core.
According to the method of manufacturing the motor disclosed in the above-described document, the permanent magnet can be fixed inside the rotor core, prevented from being detached and scattered during high-speed operation, and insulated at the same time.
However, when an adhesive is used to fix a permanent magnet to a rotor core, the adhesive may ooze to be interposed between the rotor core and each of end plates. If an adhesive is interposed between the rotor core and each of the end plates, relative motion between the rotor core and each of the end plates is restricted. Since the rotor core and the end plates are made of different materials, they have different linear expansion coefficients. The ambient temperature and heat generated as the rotating electrical machine operates cause the end plates and the rotor core to expand individually. Since the rotor core and the end plates have different linear expansion coefficients, the rotor core and the end plates change by different amounts. Consequently, compressive stress or tensile stress may originate at the rotor core along a radial direction from a portion fixed with an adhesive between the rotor core and each of the end plates. Therefore, if the rotor core is made of a plurality of stacked magnetic steel sheets, for example, a magnetic steel sheet placed at an end in an axial direction may deform.
In the method of manufacturing the motor disclosed in the above-described document, an adhesive is used to fix a permanent magnet to a rotor core, which may cause the problems above.